The airport’s worried manager, Ed Wallis, tried different treatments before he was advised to consult with officials at the Blue Plains Advanced Water Treatment Plant, a sprawling facility at the southern tip of the District that processes 375 million gallons of the area’s wastewater per day.

Airport officials liked what they saw and began accepting a dark substance called a biosolid from Blue Plains. Five months later, grass started to sprout. A year later, it was thigh-high."